1. Field of the Invention
The present invention relates to an equipment to manufacture solid surfaces with ion-using technology, and more particularly to improvements in an apparatus for etching the solid surfaces with ions in plasma.
2. Description of the Prior Art
In a semiconductor field or in a field requiring for the etching technique as fine as several microns or less, the recent increase in share is directed to the dry etching process which resorts to the use of either an ion beam or the ions or active atoms (or compounds) in plasma. As compared with the former method using the ion beam, the latter method using the ions or the like in the plasma, e.g., the RF (Radio Frequency) sputter etching method or the microwave plasma etching method has a higher ion density so that it is featured by a higher etching rate. Therefore, there have been made a variety of investigations, among which a method for generating the plasma with the use of microwave discharge is found especially excellent because: (1) since the discharge can be broken down even under a low pressure (which is lower than 1.times.10.sup.-3 Torr), the direction of the ions is uniform; (2) it is possible to generate the plasma of especially high density; and (3) since the discharge is broken down without any electrode, the sample can be prevented from having its surface contaminated, and active gases can be used (e.g., U.S. Pat. No. 4,101,411).
However, the microwave plasma etching process has a fault that its etching rate is lower than that of the RF sputter etching process which has been frequently used according to the prior art. This is because the sample in the microwave plasma etching apparatus at the initial stage is held under a floating potential (about -20 volts) with respect to the plasma.
In order to eliminate this fault, therefore, there has been made a proposal, in which a higher negative potential than that floating potential is impressed upon the sample. More specifically, if the sample is supplied with a negative voltage from the outside, the ions are accelerated to impinge upon the sample surface so that the etching rate is increased.
As a result, in case the sample is made of a conductor, the etching rate can be increased by the method described in the above. Here, the sample to be etched in a semiconductor process has its surface made of an insulator such as a film of SiO.sub.2 or a photo-resist. Consequently, the insulating surface is charged up by the ions. As a result, the negative voltage impressed upon the sample from the output is offset to apply no voltage to the sample so that the etching rate cannot be finally increased.